Rollup merge of #99573 - tbodt:stabilize-backtrace, r=yaahc

Stabilize backtrace

This PR stabilizes the std::backtrace module. As of #99431, the std::Error::backtrace item has been removed, and so the rest of the backtrace feature is set to be stabilized.

Previous discussion can be found in #72981, #3156.

Stabilized API summary:
```rust
pub mod std {
    pub mod backtrace {
        pub struct Backtrace { }
        pub enum BacktraceStatus {
            Unsupported,
            Disabled,
            Captured,
        }
        impl fmt::Debug for Backtrace {}
        impl Backtrace {
            pub fn capture() -> Backtrace;
            pub fn force_capture() -> Backtrace;
            pub const fn disabled() -> Backtrace;
            pub fn status(&self) -> BacktraceStatus;
        }
        impl fmt::Display for Backtrace {}
    }
}
```

`@yaahc`

compiler/rustc_errors/src/lib.rs

@@ -4,7 +4,6 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(drain_filter)]
-#![feature(backtrace)]
 #![feature(if_let_guard)]
 #![cfg_attr(bootstrap, feature(let_chains))]
 #![feature(let_else)]